Brakes of the type stated at the outset are known, e.g. from EP 694 707 B3. The offsetting of the axis of the holding-down clip by means of the eccentric positive support in the brake caliper in order, by means of the positive engagement in the holding-down springs shaped specifically for the purpose, to exert not only the radial but also a tangential preload on the brake pads is characteristic of the prior art brakes.
The basic principle of radial and tangential preloading has proven its worth and is to be retained. According to the invention, however, design changes and functional changes are made to the brake caliper and to the relevant parts of the holding-down system in order to achieve greater economy and greater versatility.
FIGS. 1 and 2 show the brake according to EP 694 707 B3. Here, FIG. 1 shows a brake pad 11, which is guided and supported radially inward and on both sides in the circumferential direction in a well-type guide in the brake caliper or brake support plate and on the radially outer edge of which a holding-down spring formed symmetrically on both sides relative to the central axis thereof is supported. Centrally, the holding-down spring has a central region 3 which is radially lower-lying, from which the spring legs 6, 7, situated at a higher level, extend outward on both sides along the outer edge of the pad in order then to act resiliently at the ends on the brake pad when a holding-down clip 1, likewise formed symmetrically, engages positively in the central region, which is formed radially inward here.
The holding-down clip 1 is formed from round stock. The spring preload comes into effect when, as shown in FIG. 2, the holding-down clip 1 is anchored in positive-engagement openings in the brake caliper on the brake application side and is then fastened firmly but releasably on the other side by means of screw fastening on a bearing block of the brake caliper on the rim side. The holding-down clip extends over a caliper opening used for the installation/removal of the brake pads supported on both sides of the brake disc and extends in a direction toward the brake or central axis A.
In the axial direction of the brake pads, the holding-down springs are coupled to the brake pad because radial projections 12, 14 from the outer edge of the brake pad pass through elongate openings 8, 9, 10 in the spring. At the ends, the spring legs rest against further radial projections 13, 13 on the outer edge of the brake pad. The holding-down springs are designed as leaf springs.
According to the prior art, the radial and tangential preload acting on the brake pad by means of the holding-down spring is produced by the fact that the holding-down clip 1 engages positively in the radially formed central region 3 of the holding-down spring and, for its part, is always supported in the direction of the brake disc exit side in an offset manner with an axial offset x relative to the central or brake axis A in the direction of rotation of the brake disc during forward travel, with positive engagement in application-side and rim-side anchorings of the brake caliper. As a result, the corresponding spring leg is also urged in a tangential direction. For the eccentric positive support of the holding-down clip 1, the necessary cast recesses must be present in corresponding positions in the casting for the brake caliper, and these have then subsequently to be subjected to mechanical machining operations. The points of support for the holding-down clip 1 are thus formed asymmetrically on/in the brake caliper.
The brakes concerned are installed on both sides of the axle, and therefore they must also be embodied mirror-image fashion. This means that different casting model embodiments are required for prior art brake calipers for a left-hand and a right-hand brake in order to produce the asymmetrical supporting and holding regions. Accordingly, the positions for the subsequent mechanical machining on the supporting and holding regions are also different for a left-hand brake and a right-hand brake.
Another problem with conventional brakes, especially the brake according to EP 694 707 B3, is that, owing to the overall design of the brake and the spring, the holding-down spring is subject to unfavorable loads in mechanical respects.
It is the underlying object of the invention to develop the brake according to EP 694 707 B3 in such a way that the disadvantages mentioned are eliminated. In particular, it is the underlying object of the invention to configure the holding-down spring in such a way that it is subject to lower mechanical loads in operation.
According to the invention, the stated object is achieved, in the case of a caliper disc brake of the type stated at the outset, by virtue of the fact that the holding-down spring has two identical spring legs and a trapezoidal central region which is located in between and projects radially inward, wherein the two legs of the trapezoidal region each enclose an angle of more than 95° with the base in the relaxed state and an angle of less than 85° with the respectively adjacent spring leg.
This embodiment of the holding-down spring is mechanically particularly advantageous.
According to the invention, provision is preferably made, in the relaxed state, for the holding-down spring in each case to extend in an arc with a radius of 10 mm to 16 mm in the transitional region between the two legs of the trapezoidal region and the base thereof and in an arc with a radius of 4 mm to 9.5 mm in the transitional region between the trapezoidal region and the spring legs.
Considerable mechanical advantages are also achieved by this means.
As another preferred option, it is envisaged that the holding-down spring is symmetrical and, owing to the symmetry, can be installed in two installation positions rotated by 180° relative to one another.
Mix-ups are thereby avoided.
Another preferred option according to the invention is that the holding-down spring is a leaf spring.
According to another preferred embodiment of the invention, it is envisaged that the holding-down device rests on the holding-down spring by means of a bead-shaped first region to produce the radial preload and rests on said spring by means of a second region to produce the tangential preload, and the distance between the central point of the first region and the central point of the second region is smaller in a radial direction than in a tangential direction.
This embodiment once again contributes to the relief of mechanical loads on the holding-down spring.
In addition to the caliper disc brake described in detail above, the invention also provides a related holding-down spring.
Further aspects of the invention are explained in greater detail below by means of preferred illustrative embodiments with reference to the attached drawings. The drawings are provided for purely illustrative purposes and are not intended to limit the scope of the present invention.